Functionality of Zemax OpticStudio Software

Zemax OpticStudio is a ray-tracing software which allows the user to define the geometry and material properties of their optical device, and predicts how it will interact with the light source by ray tracing methods. OpticStudio provides two primary functions; sequential and non-sequential ray tracing [37]. Sequential ray tracing analyzes a series of optical devices and their interactions with light in sequence, whereas non sequential analysis can be used for optical features in any position, sequence and orientation. The non-sequential functionality permits the analysis of complex optical devices, such as the waveguide in consideration, thus the OpticStudio Non-Sequential

Component (NSC) Editor is used.

Figure 3.1 This image depicts the Zemax user interface as well as the key parameters used to import CAD components, and define their properties.

Since Zemax permits the import of CAD models to replicate the waveguide geometry, all significant geometrical modelling is done in SolidWorks and imported into OpticStudio in STEP format. This is done by creating a new Zemax object in the NSC editor, seen in Figure 3.1, and defining it as a “CAD Part: STEP/IGES/SAT”, which permits the selection of the appropriate STEP file of the SolidWorks model. For each imported file, the desired material must be assigned to the part, if no material is assigned, the default material is air. It is thus necessary that each layer of the waveguide is imported as a separate part in order to apply different refractive indices to each layer. Using the x-, y-, and z-position parameters the layers may positioned with respect to one another to ensure proper orientation. Additionally, the position, size and orientation of particular feature geometries can be modified in Zemax. This is especially beneficial when considering the optimization of the waveguide geometry, as multiple variations can quickly be modelled and simulated, in order to investigate their impact on performance.

With the geometry imported from the CAD files, and the material properties applied, a light source must be defined for the simulation. The light source used for the majority of the simulations was a rectangular source, however in some cases a source object or source file is used. A source file is especially beneficial when examining only the diffuser region of the waveguide, as the concentrator’s illumination pattern can be replicated with a source file, rather than modelling the entire concentrating region. In most cases, the source rectangle is appropriate as it provides illumination for the entire collecting region, whether it be as an overhead source, or a discretized, curved source. Once again the component must be positioned and oriented with respect to the existing components, and the source properties must be applied.

Figure 3.2 The Non-Sequential Component editor permits the definition of a rectangular source, its total power, size and location.

The most important properties in consideration of a source are the number of rays, the total power, and the size of the source rectangle, as identified in the NSC Editor shown in Figure 3.2. There are two ray sets which must be defined; layout rays and analysis rays. Layout rays represent the rays which will be illustrated in a ray-tracing image of the waveguide, while analysis rays are the ray set which are used for the computation of ray paths and the final detector data. Typically, a much lower number of rays is used for the layout set, as this is simply a visual representation, while the analysis should be significantly more thorough; the number of analysis rays used will dictate the of the detector illumination data. In this case 10 layout rays are used, compared to 1,000,000 analysis rays.

Additionally, the total power of the source, and the size of the rectangle must be defined. In this case a total source power of 1 Watt is used in order to simplify calculations, and facilitate comparisons between number of rays and the waveguide’s efficiency. The source rectangle’s size is equivalent to the size of the collecting region in

order to be able to compute the ability of the waveguide to successfully capture illumination which strikes the concentrating features.

Finally, in order to be able to meaningfully interpret the results, detector components must be defined. Detector data permits the analysis of illumination patterns, illumination intensity, and component efficiency, thus their data is essential to the design process. For this analysis detector rectangles are used, and as before the position, orientation and size may be defined in accordance with the existing components. Also important for the definition of the detector components are the number of pixels-as this defines the resolution of the results-and the colour of the data. In this case the colour “1” is selected as this represents the data in greyscale with the most intense illumination as the brightest, and least intense illumination in black.

In the above example, five detectors are used in order to evaluate the waveguide’s performance; four of which surround the concentrating region, and the last of which covers the entire top face of the waveguide. The four detectors on the boundaries of the concentrating region are able to detect how much incident light is collected by the concentrator, by comparing the total power from these detectors, to the total incident power. The fifth detector permits the analysis of the waveguide as a whole, by determining what proportion of the incident light is successfully diffused out the illuminating region of the waveguide, as well as noting distribution and intensity of illumination. Since the fifth detector is located on the surface of the waveguide, the incident light would illuminate the centre of the waveguide, rendering the data meaningless. To mitigate this effect, Zemax permits the detector to ignore the rays on layout, and this feature is applied to ensure all illumination detected is via the waveguide’s features, as illustrated in Figure 3.3.

Figure 3.3 Zemax facilitates the definition of detectors and the relevant properties.

Two Zemax tools were primarily used to evaluate the performance of a particular waveguide design; the NSC 3D layout, and the detector viewer. The 3D layout provides a visual representation of the imported geometry, the layout rays and any other components, as defined. This tool is suitable for quick, visual analyses of a particular design, as they allow the user to determine if the rays follow the desired path. The detector viewer, while not demonstrating the ray path, gives much more detailed data than the 3D layout. The detector data evaluates the location of each ray, and predicts which pixel it will strike on the detector. Each pixel is coloured according to the illumination intensity at this location, based on how many rays struck a particular location. Additionally, the detector data provides numerical data for each pixel, as well as maximums and averages for the illumination intensity. The ray tracing image, and detector data for the above example are shown in Figure 3.4.

(a) NSC 3D layout depicts the ray trace through the optical device.

(b) Zemax detector viewer depicts illumination pattern, and includes numerical data.

Figure 3.4 Zemax represents the ray trace data in the 3D layout, providing a visual representation of the results. The detector data gives a more detailed view of the illumination patterns and extensive numerical data.

Interpretation of the detector data permits the calculation of the key performance parameters, as discussed above. The efficiency of the entire waveguide, or a portion thereof, can be calculated by dividing the power measured on a particular detector, by the total source power, to determine efficiency according to Equation 3.2. Similarly, the uniformity of a detector region can be calculated according to Equation 3.3 with the peak incoherent irradiance given in the detector data, and the average irradiance calculated by dividing total power by total area. With the method to calculate the efficiency and uniformity of any waveguide defined, Zemax provides the necessary irradiance data to evaluate and compare the illumination results of various designs.